Dodson and Amigo TRA hall is small but could perhaps work. Their TRA is now defunct, so they are looking for uses for the hall. You could certainly get it very cheap! The person to contact would be Ian Brinley who looks after community premises at Southwark.
His email is ian.brinley@southwark.gov.uk.
The hall is just off Waterloo Road, not far from the station or from Lambeth North tube.

The Draper Hall here at The Elephant is available to hire some evenings along with a 'therapy' room for professional sports/therapeutic massage, or one-on-one counselling.
DraperEstate.com
Visit our website for details.